Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

2. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

3. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

4. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Normal cooling

Super-cooling

None of these

5. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Equal to unity

Always less than unity

Any one of the above

6. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

7. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

8. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

9. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.6

0.67

0.4

10. Freon group of refrigerants are

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

Toxic

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11. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

Compressor and condenser

12. Which of the following cycles uses air as the refrigerant?

Ericson

Bell Coleman

Stirling

Carnot

13. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Rankine

Reversed Carnot

14. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

8 bar

30 bar

2 bar

15. Most thermostatic expansion valves are set for a superheat of

10°C

5°C

20°C

15°C

16. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

17. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

18. For obtaining high COP, the pressure range of compressor should be

High

Any value

Low

Optimum

19. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

1: 3

9: 1

20. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

High risibility with oil

Large latent heat

Low boiling point

Page 3 of 4

21. The boiling point of ammonia is

-33.3°C

-30°C

-10.5°C

-77.7°C

22. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Carbon dioxide

Freon

Ammonia

23. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

24. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Zero

Negative

Positive

25. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

Absorber

26. Rating of a domestic refrigerator is of the order of

5 tons

10 tons

40 tons

0.1 ton

27. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

28. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

29. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

30. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

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31. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

32. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

3.33

1.33

4.33

33. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

34. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Three heat exchangers

Four heat exchangers

35. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will evaporate

Water will never evaporate

A gas will never liquefy

36. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

37. The capillary tube, as an expansion device, is used in

Domestic refrigerators

All of these

Water coolers

Room air conditioners

38. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-135.8°C

-77.7°C

39. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

40. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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